This invention relates to a process controller and more particularly, relates to a controller for a process requiring feedback operation, with the controller being highly distributed in the sense that each mechanical or electro-mechanical operation involved in the process is independently controlled at the location of the device to be controlled.
Automatic process and related controllers having electronic feedback operation of mechanical and related devices have been used in the prior art. Examples include such simple devices as thermostats designated to control a single parameter such as temperature, and range to far more complicated devices using a main frame or mini computer to monitor and control large numbers of parameters. In the later circumstances, process controllers have typically been configured with a single central processing unit receiving data from a large variety of sources. The CPU processing the data and then uses that data to operate a large number of controlled devices.
In the prior art, process and related controllers have rarely been highly distributed. For example, when large main frame or mini-computer systems have been used, all data processing is conducted at a single location and decisions by the data processing unit to vary a controlled device are made by the central processing unit. Only when relatively simple control systems are used, such as thermostats, have "process" controllers been highly distributed. In those instances, the controllers have been highly restricted in their ability to monitor and control, in a coordinated fashion, multiple parameters. Usually, only a single parameter has been controlled by a distributed controller, or at best two or three.
Centrally operated process controllers have in the past been used with direct digital control allowing the digital commands from a conventional main frame or mini-computer to be used to control, after signal processing through a digital to analog converter, one or more devices. The limited distributed controllers, have however not been digital controllers but, as in the case of thermostats, have exclusively been analog systems.
Direct digital control systems in the past have typically incorporated a central control system, usually the computer's single processing unit. To increase flexibility, prior art direct digital control units have used a plurality of field panels multiplexed to the central processing units. Each field panel allowed adjustment of parameters to be monitored and controlled, usually for a process conducted in a particular sector. In a few circumstances, individual field panels have been replaced with small microcontroller based central processing units, allowing distribution of intelligence closer to the device or parameter to be operated or monitored. However, the prior art has not included digital intelligence which is capable of monitoring and controlling a fully distributed process from the actual control point. Prior art devices which are located at the actual control point have digital intelligence which only monitors and controls discrete functions of an overall process. These devices require intervention from a central processing unit which distributes the various functions in order to perform a complete process.
Accordingly, it is an object of this invention to provide an intelligent direct digital process control system that is highly distributed at the actual location of the process to be controlled. In addition, it is an object of the present invention to provide a highly distributed process control system which is capable of coordinating a large number of parameters and device controls.
A further object of this invention is to provide such a highly distributed process control system that is extremely flexible so that the process controller can be used over a wide range of systems, including electric, pneumatic or electro-mechanical, and acting in response to a wide variety of parameters such as pressure, temperature, control setting, switch closure, or any analog or digital representation of a physical condition.